1. Field of the Invention
The invention relates to the field of electronic document scanning devices, and more particularly, to the field of document scanning devices drawing power from a peripheral bus carrying parasitic power, such as a universal serial bus power source.
2. Brief Description of the Related Art
Document scanning devices are known peripherals for computers. A conventional document scanning device assembly is a computer peripheral that includes a contact image sensor ("CIS") module, a document drive roller, and a drive motor. In conventional document scanning devices, the document drive roller remains fixed relative to the assembly and is driven by the drive motor. The CIS module is spring mounted to the assembly and must have space for vertical clearance above the CIS module so that the CIS module can move longitudinally with respect to the scanner housing. Conventional document scanning devices scan images from a document quickly and with good resolution. These scanning devices, however, do have many drawbacks.
One problem encountered by conventional document scanning devices is torque twisting, and is further illustrated in FIG. 1a. Conventional document scanning devices include a CIS module 10 with scanning lenses 10a, movably attached to a housing 15 through a spring 12, and include a document drive roller 20 that contacts the lenses 10a of the CIS module 10.
When a document is scanned in conventional document scanning devices the document drive roller 20 rotates to feed a document through the scanner. As the document drive roller 20 rotates, the force applied to the lenses 10a of a CIS module 10 induces a torque on the CIS module 10. The torque on the CIS module 10 causes the CIS module 10 to rotate because it is movably coupled to the housing through the spring 12. The CIS module 10 rotates until the sides of the CIS module 10 impact against the housing 15 of the assembly. The rotation of the CIS module 10 causes the required motor torque to drive the document drive roller 20 to increase because of a wedging effect on the rotated CIS module 10. Increasing the motor torque to drive the document drive roller 20 increases the power draw required to operate the document scanning device.
Another problem associated with conventional document scanning devices also arises from this scanning operation and is illustrated in FIG. 1b. The lenses 10a of the CIS module 10 are positioned at a desired contact point 11 that is shown aligned with a center of the document drive roller 20. When a document is scanned and the CIS module 10 is rotated as a document is drawn through the assembly, the lenses 10a of the CIS module 10 begin to shift away 11' from the desired contact point 11 in a scanning operation. Thus, because the lenses 10a of the CIS module 10 are not aligned at the desired contact point 11, the scanning resolution is negatively affected.
Yet another problem with conventional document scanning devices is that the power draw required for a scanning operation is much greater than parasitic power available through a peripheral bus such as universal serial bus specifications. Recent computer industry trends have introduced the universal serial bus as the peripheral connection port of choice for computer and peripheral manufactures and end users. The universal serial bus is a specification developed by Intel, Microsoft, and others and used by the likes of IBM, Compaq, Dell, and other computer manufactures.
Specifically, the universal serial bus provides a single peripheral connection point on a computer that includes data communication connections and power connections. Thus, a peripheral connected to a universal serial bus connection point would not require a separate power source for operation if the power required does not exceed the power supplied by the connection point. As such, most conventional peripherals, such as conventional document scanning devices, are unsuitable for use with the universal serial bus because their current designs require greater power than that available through the universal serial bus.
Therefore, there is a need for a document scanning device that produces a high quality document scan and that may draw power from a peripheral bus, such as a universal serial bus, that provides parasitic power and that has a minimized power load with a maximum torque for scanning documents.